1. Field of the Invention
The present invention relates to a filter, or screen, for preventing the ingesting of foreign debris into a vacuum breaker valve used in a liquid piping system.
2. Description of the Related Prior Art
A liquid piping system is under a positive pressure when liquid is flowing through the system from the liquid source to a user of the liquid. When the liquid flow is stopped and pressure within the system is suddenly reduced, a negative pressure can be created within the system which can cause a backflow condition known as back siphonage from the liquid user back to the liquid source. If the piping system happens to be a water pipe delivering water from a potable water source to a water user, and the user is in communication with non-potable water, a back siphonage condition can cause non-potable water to be introduced into the potable water supply.
A number of devices and systems have been developed for preventing back siphonage. One commonly used device is a vacuum breaker which prevents back siphonage by venting the piping system, thus preventing the creation of a vacuum within the system which can create a backflow condition. Typical vacuum breakers include atmospheric vacuum breakers and pressure vacuum breakers. Atmospheric vacuum breakers have a disc float assembly comprising a float, slidably movable on a post, which seals off an atmospheric vent area when the system is pressurized, and falls under its own weight when the system is no longer pressurized to open the atmospheric vent area and allow air to enter the piping system to interrupt a possible back siphonage action. Pressure vacuum breakers are also designed to prevent back siphonage using a check valve designed to close with the aid of a spring when the water flow stops. The air inlet valve of the breaker opens when the internal pressure of the piping system drops, thus preventing possible back siphonage.